1. Field of the Invention
This invention relates to an inkjet recording apparatus.
2. Description of Related Arts
In an inkjet apparatus, in order to realize a high quality recording, the ink dot diameter needs to be made small. As a method of reducing the recording dot diameter, it is conventionally known to utilize a “pull-push driving” system where a pressure chamber communicating to a nozzle opening is contracted after temporarily expanded {(please refer to Unexamined Japanese Patent Application Publication HEI11-268266 (JPA1999-268226), and Unexamined Japanese Patent Application Publication 2004-82425 (JPA2004-82425)). According to this system, the mass of each ink droplet can be reduced, and the recording dot diameter can be minified.
In JPA1999-268226 and JPA2004-82425 a method is disclosed where after an ink meniscus is once pushed-out by a contraction pulse, the meniscus is drawn deeply into a nozzle, and thereafter a droplet is ejected, according to the “pull-push driving” system.
As the recording heads utilizing piezoelectric elements as pressure generation devices, there are: a system of applying a vibration plate described in JPA1999-268226 (for example, a laminated piezoelectric layer method, and a deflection mode method), and a shear deformation system where a partition wall of a pressure chamber is shear deformed, but not using the vibration plate.
Drive signals described in JPA1999-268226 and JPA2004-82425 require an analogue circuit for utilizing a slope waveform as a contraction pulse to push-out the meniscus, which complicates the configuration of the drive circuit. Further, since this method requires a relatively long drive period, drive frequency is difficult to be increased.
In the laminated piezoelectric layer method, which changes the volume of the pressure chamber via the vibration plate, described in JPA1999-268226, since the piezoelectric element is disposed outside the pressure chamber, the shape and size of the piezoelectric element is not so much restricted, and it is possible to generate high pressure by using a powerful piezoelectric element, thus this method is good at ejection capability and ejection control of the ink droplet. However, the structure of such an inkjet head becomes complicated, manufacturing of a large capacity head is difficult, and a head having about 100 channels may be a limit.
In contrast, since the head of shear deformation mode system, described in JPA2004-82425, has a simple structure where grooves are formed to be pressure chambers in a piezoelectric element, a large capacity head having several hundred channels is possible to be manufactured. However, especially in the cases where drive signals of a rectangular pressure wave are applied to the recording head of shear mode system, ejection of a minute droplet is difficult due to the influence of pressure wave vibration in the pressure chamber.
In the recording head utilizing a piezoelectric element as a pressure generation device, particularly in the recording head of a shear mode system, in order to effectively draw-in the meniscus position before ejection and to eject a minute droplet while suppressing the generation of pressure waves by using a rectangular wave as the contraction pulse for pushing-out the meniscus, it is necessary to devise an improved drive method.
An objective of the present invention is to provide an inkjet recording apparatus provided with a recording head capable of stably ejecting a minute droplet by utilizing a rectangular wave which is possible to simplify the drive circuit.